An elevator installation is installed in a building or attached thereto. It essentially consists of a car which is connected by way of support means with a counterweight or with a second car. The car is moved along substantially vertical guide rails by means of a drive which acts selectably on the support means or directly on the car or counterweight. The elevator installation is used for transporting persons and goods within the building over single or several floors.
The elevator installation comprises devices for safeguarding the elevator car in the case of failure of the drive, support means or other elevator components. These safeguards usually include a number of safety measures. A first safety measure is, for example, switching-off of the elevator drive and actuation of drive brakes in order to stop the elevator car. This is usually carried out by interruption of an elevator safety circuit. A further safety measure comprises activation of safety-brake devices or corresponding safety brakes. These can, when required, brake the elevator car on the guide rails or at brake rails. The safety measures are these days increasingly controlled by so-called electronic limiters which monitor movements of the elevator car.
A method for secure detection of movement states of an elevator installation is known from patent publication EP 1602610. In that case, several movement variables are detected at different locations and compared with one another and multi-stage braking measures are initiated if impermissible deviations are ascertained.
Monitoring equipment is known from a further patent publication WO2010/107409, wherein a cleaned or filtered speed signal is calculated from a combination of speed measurement and acceleration measurement.
Similar monitoring equipment is known from patent publication JP2009/023823, wherein a cleaned speed signal is calculated from a combination of travel distance measurement and acceleration measurement. In that case, an integrator calculates speed changes between measuring points of the travel distance meter. The speeds determined from the data of the travel distance meter and speed change calculated by the integrator are added and a reset logic sets the integrator to zero on each occasion when, for example, the travel distance meter registers a measuring point.